U.S. patent number 10,196,743 [Application Number 14/646,477] was granted by the patent office on 2019-02-05 for highly abrasion-resistant anti-limescale layers with high chemical resistance.
This patent grant is currently assigned to EPG (ENGINEERED NANOPRODUCTS GERMANY) AG. The grantee listed for this patent is EPG (ENGINEERED NANOPRODUCTS GERMANY) AG. Invention is credited to Klaus Endres, Luis Genolet, Barbara Kutzky, Christian Schmidt, Heike Schneider.
United States Patent |
10,196,743 |
Endres , et al. |
February 5, 2019 |
Highly abrasion-resistant anti-limescale layers with high chemical
resistance
Abstract
The invention relates to the use of a coating of a layer
including an inorganic, glass-like matrix of an alkali silicate
and/or alkaline earth silicate or a layer including an
inorganic-organic hybrid matrix or of a double layer of a base
layer including an inorganic, glass-like matrix of an alkali
silicate and/or alkaline earth silicate or a base layer including
an inorganic-organic hybrid matrix and an alkali silicate-free and
alkaline earth silicate-free top layer including a matrix of an
oxidated silicon compound as the anti-limescale coating on at least
one metal surface or inorganic surface of an object or material.
The anti-limescale coating can be used for storage or transport
devices for water or media containing water. The anti-limescale
coating is suitable for pipelines, sand control systems or safety
valves in the conveyance of oil or gas or the storage of oil or
gas.
Inventors: |
Endres; Klaus (Homburg,
DE), Schmidt; Christian (Saarbrucken, DE),
Genolet; Luis (Saarbrucken, DE), Kutzky; Barbara
(Saarbrucken, DE), Schneider; Heike (Saarbrucken,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
EPG (ENGINEERED NANOPRODUCTS GERMANY) AG |
Griesheim |
N/A |
DE |
|
|
Assignee: |
EPG (ENGINEERED NANOPRODUCTS
GERMANY) AG (Griesheim, DE)
|
Family
ID: |
50033452 |
Appl.
No.: |
14/646,477 |
Filed: |
November 20, 2013 |
PCT
Filed: |
November 20, 2013 |
PCT No.: |
PCT/EP2013/074298 |
371(c)(1),(2),(4) Date: |
May 21, 2015 |
PCT
Pub. No.: |
WO2014/079893 |
PCT
Pub. Date: |
May 30, 2014 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20150315390 A1 |
Nov 5, 2015 |
|
Foreign Application Priority Data
|
|
|
|
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Nov 21, 2012 [DE] |
|
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10 2012 022 731 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B05D
5/08 (20130101); B32B 17/06 (20130101); C08K
3/22 (20130101); C23C 18/1229 (20130101); B32B
15/04 (20130101); C23C 18/1216 (20130101); B32B
17/061 (20130101); C23C 18/1283 (20130101); B32B
17/10091 (20130101); C23C 18/1254 (20130101); C08K
5/06 (20130101); C23C 18/1212 (20130101); C23C
18/1204 (20130101); C23C 18/122 (20130101); C23C
18/1245 (20130101); B32B 27/20 (20130101); C23C
18/1208 (20130101); C09D 5/1675 (20130101); C23C
18/1225 (20130101); C23C 18/1262 (20130101); C23C
18/127 (20130101); C23C 18/125 (20130101); B32B
17/10009 (20130101); C08K 2003/2227 (20130101); Y10T
428/265 (20150115); Y10T 428/1317 (20150115); Y10T
428/31612 (20150401); Y10T 428/266 (20150115); Y10T
428/25 (20150115) |
Current International
Class: |
C23C
18/12 (20060101); B32B 17/06 (20060101); C08K
3/22 (20060101); C08K 5/06 (20060101); C09D
5/16 (20060101); B32B 15/04 (20060101); B32B
27/20 (20060101); B05D 5/08 (20060101); B32B
17/10 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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100558833 |
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Nov 2009 |
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CN |
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202 19 218 |
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Mar 2003 |
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DE |
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10 2004 001 097 |
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Jul 2005 |
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DE |
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10 2006 018 938 |
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Oct 2007 |
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DE |
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10 2007 059 423 |
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Jun 2009 |
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DE |
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10 2008 011 413 |
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Sep 2009 |
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DE |
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10 2010 011 185 |
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Sep 2011 |
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DE |
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0 113 189 |
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Jul 1984 |
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EP |
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2 757 501 |
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Jun 1998 |
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FR |
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2 806 427 |
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Sep 2001 |
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FR |
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2005/066388 |
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Jul 2005 |
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WO |
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2009/130288 |
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Oct 2009 |
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WO |
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2011/069663 |
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Jun 2011 |
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WO |
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Other References
Jun. 30, 2016 Office Action issued in European Partent Application
No. 13826841.2. cited by applicant .
Howland et al., "The Formation of Scale from Hard Waters at
Temperatures Below the Boiling Point," J. Appl. Chem., Jul. 1951,
vol. I, pp. 320-328. cited by applicant .
Jun. 20, 2014 International Search Report issued in International
Application No. PCT/EP2013/074298. cited by applicant .
May 25, 2015 International Preliminary Report on Patentability
issued in International Application No. PCT/EP2013/074298. cited by
applicant.
|
Primary Examiner: Aughenbaugh; Walter
Attorney, Agent or Firm: Oliff PLC
Claims
The invention claimed is:
1. An anti-limescale coating on at least one metal surface or
inorganic surface of an object or material, wherein the
anti-limescale coating is made of: a layer comprising an
inorganic-organic hybrid matrix; wherein the inorganic-organic
hybrid matrix is a matrix of two interpenetrating polymers, the
polymers being an inorganic condensate and an organic polymer,
representing an interpenetrating polymer network (IPN).
2. The anti-limescale coating according to claim 1, wherein the
layer further comprises one or more fillers or pigments.
3. The anti-limescale coating according to claim 2, wherein the
particle diameter (d.sub.50 value), averaged with respect to the
volume, of the filler or the pigment is within the range of 1 to 20
.mu.m.
4. The anti-limescale coating according to claim 1, wherein the
object or the material with a metal surface or inorganic surface is
a storage or transport device for water or media containing
water.
5. The anti-limescale coating according to claim 1, wherein the
object or the material is a boiler, a tank, a pipeline or a
valve.
6. The anti-limescale coating according to claim 1, wherein the
layer thickness of the layer comprising an inorganic-organic hybrid
matrix is no greater than 20 .mu.m; or one or more intermediate
layers are arranged between the metal surface or inorganic surface
and the anti-limescale coating.
7. The anti-limescale coating according to claim 2, wherein the
proportion of fillers and/or pigments in the layer comprising an
inorganic-organic hybrid matrix is in the range from 1 to 35% by
weight, based on the total weight of the layer.
8. The anti-limescale coating according to claim 1, wherein the
anti-limescale coating is made of the layer comprising an
inorganic-organic hybrid matrix, and is obtained by wet-chemical
application of a coating composition on at least one metal surface
or inorganic surface of the object or the material and hardening
the coating composition, the coating composition comprising a
heterocondensate and an organic monomer, oligomer or polymer, which
comprises at least one polymerisable group, and the
heterocondensate is a metallosiloxane or borosiloxane and contains
heteroatom units of heteroatoms selected from B, Al, Ga, In, Tl,
Ge, Ga, Sn, Pb, Ti, Zr, Hf, Sc, Y and La, which are incorporated in
the siloxane skeleton by means of oxygen bridges, and siloxane
units, in which the silicon atom has a non-hydrolysable organic
group.
9. A storage or transport device for water or media containing
water with an anti-limescale coating on at least one metal surface
or inorganic surface of the storage or transport device, wherein
the anti-limescale coating has a layer comprising an
inorganic-organic hybrid matrix, wherein the inorganic-organic
hybrid matrix is a matrix of two interpenetrating polymers, the
polymers being an inorganic condensate and an organic polymer,
representing an interpenetrating polymer network (IPN).
10. The storage or transport device according to claim 9, wherein
the device is a boiler, a tank, a pipeline or a valve.
11. A method for transporting or storing water or a medium
containing water, wherein the water or the medium containing water
is transported by an object or is stored in an object, wherein the
object comprises at least one metal surface or inorganic surface,
which has an anti-limescale coating made of a layer comprising an
inorganic-organic hybrid matrix, wherein the inorganic-organic
hybrid matrix is a matrix of two interpenetrating polymers, the
polymers being an inorganic condensate and an organic polymer,
representing an interpenetrating polymer network (IPN).
12. The method according to claim 11, wherein the object is in a
conveying system, in which water-containing oil or gas is conveyed
or transported.
13. The anti-limescale coating layer of claim 8, wherein the
silicon atom has a non-hydrolysable organic polymerisable
group.
14. The anti-limescale coating according to claim 1, wherein the
filler or the pigment is selected from at least one of abrasive
fillers, solid lubricants and colour pigments.
15. The anti-limescale coating according to claim 4, wherein the
object or the material with a metal surface or inorganic surface is
a storage or transport device for media containing water, and the
medium containing water is water-containing crude oil or natural
gas.
16. The anti-limescale coating according to claim 5, wherein the
object or the material is a safety valve, which is used for
conveying oil or gas or storing oil or gas.
Description
The invention relates to the use of special layers as
anti-limescale layers, storage and transport devices for water or
water-containing media such as water-containing crude oil or
natural gas, which have such anti-limescale layers, and to a method
for transporting or storing water or water-containing media.
Limescale deposits or buildups of limescale are a precipitation of
insoluble carbonates and sulphates from hard water, attaches to the
inside of boilers, pipelines or valves, for example safety valves,
as fixed crusts. The limescale deposit and the associated damage to
the boiler or pipe wall or the valves can lead to dramatic damage
through to functional failure of the equipment and components.
The production of limescale deposits on metal or ceramic surfaces
depends on several factors, which are described, for example, in A.
H. Howland et al., J. Appl. Chem. 1951, pages 320-327. In addition
to the contents such as, for example, salts such as CaCO.sub.3,
which are contained in the water, their solubility behaviour, the
nucleation and the crystal growth also, of course, play a decisive
role during the buildup of the coating layers. A further decisive
parameter is the chemical, physical or mechanical adherence of the
contamination to the surface.
While the contents in the water can generally not be influenced in
many applications, the other parameters can be influenced with a
suitable coating. The fewer crystallisation nuclei that are present
or formed on the surfaces, the smaller is the formation of a
coating layer. If a limescale covering layer should nevertheless
form, this can be removed more easily from the surface in the case
of poor adhesion. This poor adhesion can be achieved by surfaces
that are as smooth as possible, so a smaller true surface is
achieved and the possibility of settling in pores, holes or
scratches is reduced or eliminated, and can above all be achieved
by preventing chemical adhesion.
Anti-limescale coatings are coatings on a surface, which, in
comparison to the surface without an anti-limescale layer of this
type, reduce or prevent limescale deposits on the surface and/or
allow a facilitated removal of limescale covering layers that have
been produced.
Possible coating materials, which satisfy the above-mentioned
requirements, are principally metal coatings, which are applied
galvanically or by vacuum techniques, or ceramic layers. In the
case of metallic coatings, hard temperature-resistant layers can be
produced, which are generally, however, non-transparent and special
systems, the integration of which in production sequences is
expensive, have to be available to apply them.
Non-oxidated materials, especially, appear suitable in the case of
ceramic layers. These extremely hard and abrasion-resistant layer
materials lead to a smoothing of the metal surface and, because of
the non-oxidated character, to poor attachment of the limescale
coating layers. However, complex and expensive equipment is
required for application, which takes place by means of CVD or
PVD.
Thin, transparent glass-like layers based on sol-gel systems and
nano-scale systems can be produced by means of wet-coating methods.
A coating technology is described in DE-A-10 2004001097 or
WO-A-2005066388, with which thin layers of only a few .mu.m can be
obtained on metal surfaces. Despite this small thickness, the
layers are very abrasion-resistant and cannot be scratched, for
example with corundum-containing scrubbing sponges. Layers of this
type, which allow the production of inorganic crack-free coatings
on glass and metal, in contrast to the inorganic layers described
in the prior art, in which a critical layer thickness of a maximum
of 100 to 300 nm can be achieved, can achieve layer thicknesses of
up to 10 .mu.m.
Thus, a coating system for high-grade steel 1.4301 is known, which
allows crack-free transparent glass-like layers with a layer
thickness of about 5 .mu.m.
The layers do not exhibit any visible or measurable abrasion after
1,000 cycles of the Taber abrasion test (friction wheel CS-10F,
load 500 g).
The drawback in these materials is their inadequate hydrolytic
stability for certain applications, especially at relatively high
temperatures and their inadequate abrasion resistance for certain
applications; in other words, materials of this type have limited
resistance in acidic but, especially, in alkaline media. The layer
materials described above may, for example, be dissolved in diluted
caustic soda at a slightly elevated temperature. Thus, layers of
this type can only be used to a limited extent for application
under elevated temperatures and in alkaline media.
As is known from the published sol-gel literature, the chemical
resistance of such layers can be improved by the use of ions, which
act as crosslinking catalysts. These may, for example, be iron,
aluminium, zirconium or titanium. However, additives of this type,
as also known from the sol-gel literature, influence the processing
properties of the coating paints owing to their catalytic
crosslinking acceleration.
The aim of the invention was to provide a coating system as an
anti-limescale coating for metal or ceramic surfaces, which reduces
or prevents the attachment and buildup of limescale deposits and/or
allows easier removal of limescale coating layers that have been
produced. The coating system is also to allow a transparent,
translucent or coloured coating and is to be able to be applied by
means of a wet-chemical coating method. Moreover, it should be made
possible to use coatings of this type in media, in which a high
hydrolytic stability is required. Moreover, the coating system is
to have a high abrasion resistance.
Surprisingly, it was possible to address the aim by using a coating
of a layer comprising an inorganic, glass-like matrix of an alkali
silicate and/or alkaline earth silicate or a layer comprising an
inorganic-organic hybrid matrix or of a double layer of a base
layer comprising an inorganic, glass-like matrix of an alkali
silicate and/or alkaline earth silicate or a base layer comprising
an inorganic-organic hybrid matrix and an alkali silicate-free and
alkaline earth silicate-free top layer comprising an inorganic,
glass-like matrix of an oxidated silicon compound as the
anti-limescale coating on at least one metal or inorganic surface
of an object or material. The layer comprising an inorganic,
glass-like matrix of an alkali silicate and/or alkaline earth
silicate especially preferably comprises one or one or more fillers
or pigments. A layer of this type is also called a composite layer
here, as it comprises a composite of the inorganic, glass-like
matrix and the filler or pigment.
Surprisingly, the coating is distinguished by a high anti-limescale
effect. In the case of a calcification test on metallic components,
it was possible to show that by using the above-mentioned
anti-limescale coating, the calcification can be significantly
reduced. Thus, the limescale deposit which, in uncoated components,
was 3.5 g after 300 test cycles, could be reduced to 0.4 g in the
case of coated components. Without wishing to commit to a theory,
it is assumed that this can be attributed inter alia to a
planarising effect of the anti-limescale layer and to the changed
contact angle of the layer surface. The contact angle can be
increased to 78.degree. by the anti-limescale coating in comparison
to the uncoated component, which has a contact angle of
48.degree..
Surprisingly, these systems are distinguished by high hydrolysis
resistance, especially when the layer comprising an inorganic,
glass-like matrix furthermore comprises at least one filler and/or
at least one pigment. As the layer or the double layer can be
wet-chemically applied, the production is also simple and
economical, and objects or materials with a complex geometry can
also be provided with the anti-limescale coating.
The anti-limescale coating can also be produced virtually
transparently and intermediate layers can be inserted between the
metal surface or the inorganic surface and the anti-limescale
coating. Thus, colour effects can be produced as required by
absorbing corresponding colouring means in the anti-limescale layer
itself, especially in the layer comprising an inorganic, glass-like
matrix of an alkali silicate and/or alkaline earth silicate or in
the optional intermediate layer. Moreover, the layers can be very
thin.
Very good results were achieved when the coating compositions
described in DE-A-102004001097 or in DE-A-102010011185 are used for
the formation of the inorganic, glass-like matrix, i.e. both for
the layer comprising an inorganic, glass-like matrix of an alkali
silicate and/or alkaline earth silicate and for the optional alkali
silicate-free and alkaline earth silicate-free top layer comprising
and inorganic, glass-like matrix of an oxidated silicon compound.
The methods described there for thermal compression for these
layers have also proven to be expedient. The coating composition
described there for the inorganic, glass-like matrix and the method
steps for application and for the thermal compression are therefore
adopted here by reference. The invention will be described in
detail below.
All objects or materials that consist of a metal or an inorganic
material or comprise at least one metal surface or inorganic
surface, for example objects or materials of another material,
which is provided, on at least one surface, with a metal layer or
inorganic layer or a metal component or an inorganic component, are
suitable as the object or material to be coated according to the
invention having at least one metal surface or inorganic
surface.
In this application, metal also always includes metal alloys.
Inorganic surfaces are taken to mean all inorganic surfaces here
that differ from metal surfaces. Preferred examples of inorganic
surfaces are surfaces made of ceramic or a mineral material.
Examples of objects or materials with a mineral surface are rocks,
such as gravel or grit, and sand.
The object or material with a metal surface or inorganic surface
may, for example, be semi-finished products, such as plates, metal
sheets, rods or wires, rock, particles, components or finished
products, such as boilers, tanks and, especially, pipes, sand
control systems and valves or safety valves. The object or material
can be provided completely with the anti-limescale coating on the
metal surface or the inorganic surface. Of course, it is also
possible to only provide individual regions or parts of the metal
surface or the inorganic surface with the anti-limescale coating
when, for example, only certain regions require corresponding
protection. For example, in the case of objects such as boilers,
tanks, pipe lines and valves, especially safety valves, it may
generally be sufficient if the inner surfaces or the surfaces
coming into contact with water or media containing water are
provided with the anti-limescale coating.
Examples of suitable metals for the metal surface of the object or
material are aluminium, titanium, tin, zinc, copper, chromium or
nickel, including galvanised, chrome-plated or enamelled surfaces.
Examples of metal alloys are, especially, steel or high-grade
steel, aluminium, magnesium and copper alloys, such as brass and
bronze. Metallic surfaces made of steel, high-grade steel,
galvanised, chrome-plated or enamelled steel or titanium are
especially preferably used. The ceramic surface may be made of any
usual ceramic, for example a conventional ceramic based on the
oxides SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2 or MgO or the
corresponding mixed oxides.
The metallic or inorganic surface may have a level or a structured
surface. The geometry of the object or material or the metal or
inorganic surface can be simple, for example, a simple metal sheet,
but also complex, for example with edges, rounded areas, elevated
areas or indentations. The metal or inorganic surface is preferably
cleaned before the anti-limescale coating is applied and freed of
grease and dust. Before the coating, a surface treatment, for
example by corona discharge, can also be carried out. An
intermediate layer, for example an adhesion-promoting layer or a
coloured layer to achieve optical effects, can also be applied
between the metal surface or inorganic surface and the
anti-limescale coating.
In a preferred embodiment, the layer comprising an inorganic,
glass-like matrix of an alkali silicate and/or alkaline earth
silicate or the layer comprising an inorganic-organic hybrid matrix
furthermore comprises at least one filler or at least one pigment,
wherein this is especially preferred for the layer comprising an
inorganic, glass-like matrix of an alkali silicate and/or alkaline
earth silicate. The fillers or pigments are particles. The
particles may have any desired shape. They may, for example, be
spherical, block-shaped or platelet-shaped. The person skilled in
the art knows that the particles can frequently have a more or less
irregular shape, for example when they are present as aggregates.
If no preferred directions are present, the shape of a sphere is
frequently preferred to determine the size. In the case of
platelet-shaped or scaly particles, two preferred directions are
present.
It is especially preferred that the diameter of the filler or
pigment particles or, in the case of a platelet-shaped geometry of
the filler or pigment particles, the thickness of the filler or
pigment particles is smaller than the layer thickness of the
composite layer. The size of the fillers or pigments may vary to a
broad extent depending on the anti-limescale coating used.
Expediently, the diameter of the fillers and pigments used is in
the range from 1 to 20 .mu.m, more preferably from 1.5 to 15 .mu.m,
especially preferably from 2 to 10 .mu.m and, especially, from 2.5
to 6 .mu.m.
The diameter for non-platelet-shaped fillers or pigments, in other
words, especially particles without preferred directions, is taken
to mean here the mean particle diameter based on the volume average
(d.sub.50 value). This value may, for example, be determined
laser-optically with a dynamic laser light scattering, for example
by means of a UPA (Ultrafine Particle Analyser, Leeds
Northrup).
The particle sizes of platelet-shaped fillers or pigments, i.e. the
thickness and diameter, can be determined, for example, by means of
light microscopy, by optical image valuation. As these are
platelet-shaped particles, the diameter relates to the lateral
diameter or the equivalent diameter of the circle equal to the
projection area in a stable particle position. The thickness and
diameter also signify here the mean thickness or the mean diameter
based on the volume average (d.sub.50 value).
All the conventional fillers or pigments known to the person
skilled in the art are suitable as a filler or pigment. The filler
or the pigment is preferably selected from at least one of abrasive
fillers, solid lubricants and colour pigments. A filler or a
pigment or mixtures of two or more fillers and/or pigments can be
used. Mixtures of fillers or pigments of the same material, which
differ, for example, with respect to size and/or particle shape,
can also be used. Mixtures of at least one abrasive filler and at
least one anti-lubricant, of at least one abrasive filler and at
least one colour pigment, of at least one anti-lubricant and at
least one colour pigment or a mixture of at least one abrasive
filler, at least one anti-lubricant and at least one colour pigment
can also be used.
The layer used alone or as a base layer comprises an inorganic,
glass-like matrix or an inorganic-organic hybrid matrix. Owing to
the preferred combination of this matrix with the one or more
fillers or pigments contained therein, a preferably used composite
layer is produced, which surprisingly has an excellent
anti-limescale effect, especially when the filler or the pigment is
selected from an abrasive filler, an anti-lubricant, a colour
pigment and one of the aforementioned combinations of these fillers
or pigments.
Fillers of an abrasive material are known to the person skilled in
the art and are, for example, used as an abrasive. Transparent
abrasive fillers are preferred. The abrasive fillers used, on the
basis of the Moh's hardness scale, preferably have a Moh's hardness
of at least 7 and preferably >7. The abrasive filler is
preferably a filler made of a hard substance. A general overview
and examples of abrasive materials or hard substances suitable for
the present invention are to be found, for example, in "Ullmanns
Encyclopadie der technischen Chemie", 4.sup.th edition, volume 20,
"Grinding and abrasives", pages 449-455, and volume 12, "Hartstoffe
(introduction)", page 523-524, Verlag Chemie, Weinheim N.Y.,
1976.
Examples of hard substances are carbides, nitrides, borides,
oxycarbides or oxynitrides of transition metals or semimetals, such
as of Si, Ti, Ta, W and Mo, for example TiC, WC, TiN, TaN,
TiB.sub.2, MoSi.sub.2, hard substance mixed crystals, such as
TiC--WC or TiC--TiN, double carbides and complex carbides, such as
Co.sub.3W.sub.3C and Ni.sub.3W.sub.3C, and intermetallic compounds,
such as, for example, from the systems W--Co or Mo--Be, natural or
synthetic diamond, corundum (Al.sub.2O.sub.3), such as, for
example, emery, fused corundum or sintered corundum, natural or
synthetic precious stones, such as sapphire, ruby or zirconium,
boron, cubic boron nitride, boron carbide (B.sub.4C), silicon
carbide (SiC) and silicon nitride (Si.sub.3N.sub.4), quartz, glass
or glass powder. Examples of abrasion-resistant fillers that can be
used are platelet-shaped Al.sub.2O.sub.3, platelet-shaped
SiO.sub.2, TiO.sub.2 and the like.
Preferably used hard substances are carbides, nitrides or borides
of transition metals, natural or synthetic diamond, corundum and
platelet-shaped corundum, natural or synthetic precious stones,
boron, boron nitride, boron carbide, silicon carbide, silicon
nitride and aluminium nitride, the non-metallic ones being
preferred. Especially suitable hard substances are corundum,
silicon carbide and tungsten carbide.
Pigments or fillers of a solid lubricant are furthermore suitable.
Such solid lubricants are known to the person skilled in the art
and are, for example, used as an additive in different application
areas. Especially suitable examples of fillers or pigments of a
solid lubricant are PTFE pigments, graphite pigments, molybdenum
sulphide pigments and boron nitride pigments. Metal oxides can also
be used. The filler made of a solid lubricant is preferably an
inorganic filler.
Suitable colour pigments are all conventional and known to the
person skilled in the art and generally commercially available.
Examples are white pigments, for example TiO.sub.2, black pigments,
for example carbon black, complex iron mixed oxides, coloured
pigments for all visible colours and mica pigments or interference
or effect pigments. Details are to be found, for example, in G.
Pfaff, "Industrial Inorganic Pigments" Wiley VCH, 2008 or H.
Endriss, "Aktuelle anorganische Buntpigmente", Verlag Vincentz,
1997. The pigments may, for example, be oxides, for example
spinels, rutiles, perovskites and silicates, sulphides,
oxynitrides, nitrides such as BN, carbides such as SiC or
elementary forms, for example carbon black and carbon. Effect
pigments based on mica are, for example, the known Iriodin.RTM.
pigments from the company Merck. Ceramic colour pigments are
especially suitable because of their temperature stability.
If used, the quantity of fillers or pigments in the layer
comprising an inorganic, glass-like matrix of an alkali silicate
and/or alkaline earth silicate or the layer comprising an
inorganic-organic hybrid matrix may vary within broad ranges
depending on the purpose of use. However, with the optional use of
fillers or pigments, preferred results can generally be achieved
when the proportion of fillers or pigments in the composite layer
is in the range from 1 to 35% by weight, preferably 1 to 10% by
weight and, especially preferably 1.5 to 3% by weight, based on the
total weight of the finished composite layer.
The finished layer comprising an inorganic, glass-like matrix of an
alkali silicate and/or alkaline earth silicate or an
inorganic-organic hybrid matrix and optionally one or more fillers
or pigments, after thermal compression may, for example, have a
layer thickness up to 20 .mu.m, especially preferably up to 10
.mu.m, without cracks forming during the drying and the
compression. Generally, the layer thickness of this layer is at
least 1 .mu.m, preferably at least 2 .mu.m. The layer thickness
may, for example, be in the range from 3 to 8 .mu.m.
Especially good results can be achieved when using the materials
described in DE-A-102004001097 or DE 102010011185 A1 for the matrix
of the layer comprising an inorganic, glass-like matrix of an
alkali silicate and/or alkaline earth silicate and/or the matrix
for the optionally used alkali silicate-free and/or alkaline earth
silicate-free top layer. Especially with regard to the hydrolytic
resistance of the anti-limescale coating, the double layer, which
is constructed of the specific base layer with the top layer
over-layered thereon, has achieved especially good results.
The layer used alone for the anti-limescale coating or in the
double layer as a base layer comprises, in a first alternative, an
alkaline earth silicate and/or alkali silicate as the inorganic,
glass-like matrix. The production of such inorganic, glass-like
matrices or alkaline earth silicate-containing and/or alkali
silicate-containing matrices is known to the person skilled in the
art. It is especially preferably a matrix, which was produced by
the method and with the materials as described in DE-A-102004001097
or DE-A1-102010011185.
To produce this layer, a coating composition, which comprises a
hydrolysate or condensate of a hydrolysable compound as the
glass-forming matrix precursor and optionally one or more fillers
or pigments, is preferably applied to the metal surface or
inorganic surface and thermally compressed while forming the layer.
In other words, the layer is, especially, wet-chemically applied.
If the metal surface or inorganic surface is to have one or more
intermediate layers, these are applied in the conventional manner
and the aforementioned layer applied accordingly to this/these
intermediate layer(s).
The hydrolysate or condensate of hydrolysable compounds is
preferably a coating suspension or solution, especially preferably
a coating sol, which is preferably produced by the sol-gel method
or similar hydrolysis and condensation processes.
The hydrolysable compounds preferably comprise at least one
organically modified hydrolysable silane. The hydrolysate or
condensate is preferably an alkali silicate-containing or alkaline
earth silicate-containing coating suspension or solution and
preferably an alkaline earth silicate-containing or alkali
silicate-containing coating sol.
A coating composition is preferably used as the alkali
silicate-containing or alkaline earth silicate-containing coating
suspension or solution, which is obtained by hydrolysis and
condensation of at least one organically modified hydrolysable
silane in the presence of alkali metal oxides or hydroxides or
alkaline earth metal oxides or hydroxides and optionally nano-scale
SiO.sub.2 particles.
The coating composition for the layer for the anti-limescale layer
used alone or in the double layer as a base layer is, for example,
obtainable by hydrolysis and polycondensation of one or more
silanes of the general formula (I) R.sub.nSiX.sub.4-n (I) wherein
the groups X, the same or different from one another, are
hydrolysable groups or hydroxyl groups, the groups R, the same or
different from one another, stand for hydrogen, alkyl, alkenyl and
alkinyl groups with up to 4 carbon atoms and aryl, aralkyl and
alkaryl groups with 6 to 10 carbon atoms and n signifies 0, 1 or 2,
providing that at least one silane wherein n is 1 or 2 is used or
oligomers derived therefrom, in the presence of a) at least one
alkali metal and alkaline earth metal compound, preferably from the
group of oxides and hydroxides or the organometallic compounds of
alkali metals and alkaline earth metals and b) optionally added
SiO.sub.2 particles, especially nano-scale SiO.sub.2 particles
and/or c) optionally of alkoxides or soluble compounds of the
metals B, Al, Si, Ge, Sn, Y, Ce, Ti or Zr.
The alkali metal or alkaline earth metal compound may, for example,
be a compound of Li, Na, K, Mg, Ca or Ba, wherein several can also
be used. These are preferably alkaline compounds, for example
oxides and hydroxides of alkali metals and alkaline earth metals.
These oxides and hydroxides are preferably those of Li, Na, K, Mg,
Ca and/or Ba. Alkali metal hydroxides, especially NaOH and KOH are
preferably used. Possible examples of organometallic compounds are
alkoxides of alkali metals and alkaline earth metals, for example
calcium alkoxides.
The ratio of the alkali metal and/or alkaline earth metal compound
used is preferably selected such that the alkali or alkaline earth
compound is used in a quantity such that the atomic ratio Si:
(alkali metal and alkaline earth metal) is in the range from 20:1
to 7:1, especially from 15:1 to 10:1. In any case, the atomic ratio
of silicon to (alkaline earth metal and alkali metal) is selected
to be so great that the resulting coating is not water-soluble as,
for example, in the case of water glass.
Explanations of the suitable silanes of the formula (I) follow.
Unless otherwise stated, the details including the details on the
hydrolysis and condensation conditions apply equally to silanes of
the formulas (I) and (II), which can be used for the alternative
(base) layer or the optionally used top layer.
Included in the above silanes of the general formula (I) is
preferably at least one silane, in the general formula of which n
has the value 1 or 2. At least two silanes of the general formula
(I) are especially preferably used in combination. In these cases,
these silanes are preferably used in a ratio such that the average
value of n (on a molar basis) is 0.2 to 1.5, preferably 0.5 to 1.0.
An average value of n in the range from 0.6 to 0.8 is especially
preferred.
In the general formula (I) the groups X, which are the same or
different from one another, are hydrolysable groups or hydroxyl
groups. Specific examples of hydrolysable groups X are halogen
atoms (especially chlorine and bromine), cyanates and isocyanates,
alkoxy groups and acyloxy groups with up to 6 carbon atoms.
Especially preferred are alkoxy groups, especially C1-4 alkoxy
groups, such as methoxy, ethoxy, n-propoxy and i-propoxy. The
groups X in a silane are preferably identical, methoxy or ethoxy
groups being especially preferably used.
In the groups R in the general formula (I), which in the case of
n=2 may be same or identical, these are hydrogen, alkyl, alkenyl
and alkinyl groups with up to 4 carbon atoms and aryl, aralkyl and
alkaryl groups with 6 to 10 carbon atoms. Specific examples of
groups of this type are methyl, ethyl, n-propyl, propyl, n-butyl,
sec-butyl and tert-butyl, vinyl, allyl and propargyl, phenyl, tolyl
and benzyl. The groups may have conventional substituents but
groups of this type preferably do not carry any substituents.
Preferred groups R are alkyl groups with 1 to 4 carbon atoms,
especially methyl and ethyl, and phenyl.
It is preferred if at least two silanes of the general formula (I)
are used, wherein in one case n=0 and in another case n=1. Silane
mixtures of this type, for example, comprise at least one alkyl
trialkoxysilane (for example (m)ethyl tri(m)ethoxysilane) and a
tetraalkoxysilane (for example tetra(m)ethoxysilane). An especially
preferred combination for the starting silanes of formula (I) is
methyl tri(m)ethoxysilane and tetra(m)ethoxysilane. An especially
preferred combination for the starting silanes of formula (I) is
methyl tri(m)ethoxysilane and tetra(m)ethoxysilane. (M)ethoxy
signifies methoxy or ethoxy.
The hydrolysis and condensation of the hydrolysable starting
compounds preferably takes place by the sol-gel method. In the
sol-gel method, the hydrolysable compounds are hydrolysed with
water, generally in the presence of acid or alkaline catalysts and
at least partially condensed. The acid hydrolysis and condensation
preferably takes place in the presence of acid condensation
catalysts (for example hydrochloric acid, phosphoric acid or formic
acid), for example at a pH of preferably 1 to 3. The coating
composition for the top layer is preferably produced by means of an
acid catalyst. The sol forming can be adjusted by suitable
parameters, for example degree of condensation, solvent or pH, to
the viscosity desired for the coating composition.
Further details of the sol-gel method are, for example described in
C. J. Brinker, G. W. Scherer: "Sol-Gel Science--The Physics and
Chemistry of Sol-Gel-Processing", Academic Press, Boston, San
Diego, New York, Sydney (1990).
The optional and preferred fillers or pigments are preferably
dispersed into this coating suspension or solution or the sol of
the glass-forming matrix in order to form the coating composition.
However, it is also possible to combine the fillers or pigments
with the hydrolysable compounds and to carry out the hydrolysis
and/or condensation in the presence of the fillers or pigments. The
filler or the pigment may, for example, be added directly as a
powder or as a suspension or slurry in an organic solvent to the
coating composition.
The nano-scale SiO.sub.2 particles optionally used in addition to
the hydrolysable silanes of the general formula (I) are preferably
used in a quantity such that the ratio of all the Si atoms in the
silanes of the general formula (I) to all the Si atoms in the
nano-scale SiO.sub.2 particles is in the range from 5:1 to 1:2,
especially 3:1 to 1:1. Nano-scale SiO.sub.2 particles are taken to
mean SiO.sub.2 particles with an average particle diameter of
preferably no more than 100 nm, preferably no more than 50 nm and,
especially, no more than 30 nm. Conventional commercial silica
products, for examples silica sols, such as the Levasile.RTM.,
silica sols from Bayer AG, or pyrogenic silicas, for example the
Aerosil products from Degussa, can also, for example, be used for
this.
The layer used alone for the anti-limescale coating or in the
double layer as a base layer comprises, in a second alternative, an
inorganic-organic hybrid matrix. This is a matrix of two
interpenetrating polymers, namely an inorganic condensate,
preferably an inorganic heterocondensate, and a purely organic
polymer. Such inorganic-organic hybrid systems are also called IPN
polymers (interpenetrating polymer networks). The interpenetrating
polymers can be mixed purely physically but are preferably
covalently linked with one another.
The production of such inorganic-organic hybrid matrices is known
to the person skilled in the art. This is preferably a matrix,
which is produced, for example, by methods and with materials as
described in DE-A-102006018938, DE-A-2007059423 or DE
102008011413.
To produce this layer, a coating composition, which comprises an
inorganic condensate and an organic monomer, oligomer or polymer,
which comprises at least one polymerisable group, is preferably
applied to the metal surface or inorganic surface and hardened,
especially thermally hardened while forming the layer. If the metal
surface or inorganic surface is to have one or more intermediate
layers, these are applied in the conventional manner and the
aforementioned layer is applied correspondingly to this/these
intermediate layer(s).
The condensate may be a siloxane condensate. However, the
condensate is preferably a heterocondensate, which is a
metallosiloxane or borosiloxane and contains heteroatom units of
heteroatoms selected from B, Al, Ga, In, TI, Ge, Ga, Sn, Pb, Ti,
Zr, Hf, Sc, Y and La, which are built into the siloxane skeleton by
means of oxygen bridges, and siloxane units, in which the silicon
atom has a non-hydrolysable organic group, preferably a
non-hydrolysable organic polymerisable group.
The heterocondensate is formed from silicon compounds and metal or
boron compounds, especially by hydrolysis and condensation,
preferably by the sol-gel method as described above. At least one
hydrolysable silicon compound with a non-hydrolysable organic group
is used as the Si component, which preferably has a polymerisable
radical.
The abovementioned silanes of the general formula (I) can be used
as the hydrolysable silicon compound with the non-hydrolysable
organic group. The use of at least one hydrolysable silicon
compound with a non-hydrolysable organic polymerisable group is
preferred, for example a compound of the general formula (II)
(Rx).sub.bR.sub.cSiX.sub.4-b-c (II) wherein the groups Rx are the
same or different and are hydrolytically non-splitable groups,
which comprise at least one polymerisable group, the groups R are
the same or different and are hydrolytically non-splitable groups,
the groups X are the same or different and are hydrolytically
splitable groups or hydroxy groups, b has the value 1, 2 or 3 and c
has the value 0, 1 or 2, wherein the sum (b+c) is 1, 2 or 3. In the
formula (II) b is preferably 1 and c is preferably 0, so the
polymerisable organosilane of formula (II) is preferably
(Rx)SiX.sub.3 or (Rx)R.sub.cSiX.sub.3-c.
Suitable and preferred examples of hydrolytically splitable or
hydrolysable groups X and the hydrolytically non-splitable groups R
are the same as was mentioned for the groups X or R in the formula
(I).
The groups Rx comprise at least one polymerisable group, by means
of which a crosslinking of the forming condensate with one another
or with the added organic monomers, oligomers or polymers is
possible. Examples of the polymerisable group are epoxide, such as,
for example, glycidyl or glycidyloxy, hydroxy, amino,
monoalkylamino, dialkylamino, optionally substituted anilino,
amide, carboxy, alkenyl, alkinyl, acryl, acryloxy, methacryl,
methacryloxy, mercapto, cyano, isocyanato, aldehyde, keto, alkyl
carbonyl, acid anhydride and phosphoric acid. These substituents
are bound by means of divalent bridge groups, especially alkylene
or arylene bridge groups, which can be interrupted by oxygen or
--NH-- groups, to the silicon atom. The bridge groups contain, for
example, 1 to 18, preferably 1 to 8 and especially 1 to 6 carbon
atoms. The bridge group is preferably an alkylene, especially a
propylene group. Preferred polymerisable groups, by which a
crosslinking is possible, are vinyl, acryl or acryloxy, methacryl
or methacryloxy.
Specific examples are glycidyloxypropyltrimethoxysilane (GPTS),
.gamma.-glycidyloxypropyltriethoxysilane (GPTES),
3-isocyanatopropyltriethoxysilane,
3-isocyanatopropyldimethylchlorosilane,
3-aminopropyltrimethoxysilane (APTS). Preferred examples are vinyl
silanes, acrylic silanes and methacrylic silanes, such as
vinyltriethoxysilane, (meth)acryloxyalkyltrimethoxysilane and
(meth)acryloxyalkyltriethoxysilane, especially
(meth)acryloxypropyl-trimethoxysilane and
(meth)acryloxypropyltriethoxysilane, (meth)acryloxypropyl-methyld
imethoxysilane, (meth)acryloxyethyltrimethoxysilane and
(meth)acryloxy-ethylmethyldimethoxysilane, wherein
methacryloxypropyltrimethoxysilane is especially preferred.
In preferred embodiments, apart from the at least one silicon
compound with a polymerisable group, one or more further silicon
compounds are used as the Si component, for example silanes of the
formula (I), wherein these may be hydrolysable silanes with at
least one non-hydrolysable organic group and/or hydrolysable
silanes without non-hydrolysable organic groups.
Used as a further component for the heterocondensate is an
additional compound, especially a hydrolysable compound, of an
element selected from B, Al, Ga, In, TI, Ge, Ga, Sn, Pb, Ti, Zr,
Hf, Sc, Y and La. Titanium compounds are preferred. The compounds
can be used individually or as a mixture of two or more of these
elements.
The metal or boron compound may be a compound of formula (III)
MX.sub.a (III) wherein M is B, Al, Ga, In, Tl, Ge, Ga, Sn, Pb, Ti,
Zr, Hf, Sc, Y and La, X is defined in formula (I), including the
preferred examples, wherein two groups X can be replaced by an oxo
group, and a corresponds to the valence of the element, wherein
when using complex ligands a can also be greater or, in the case of
multidentate ligands, can also be smaller than the valence of M.
The valence of M is generally 2, 3 or 4. Optionally, the compound
of formula (III) also comprises a counterion. X, apart from the
substituents given in formula (I) can also be a sulphate, nitrate,
a complexing agent, such as, for example, a .beta.-diketone, a
saturated or unsaturated carboxylic acid or the salt thereof, an
inorganic acid or a salt thereof and an amino alcohol. The metal or
boron compound is preferably a hydrolysable compound. Metal or
boron alkoxides are preferred.
The alkoxides of Ti, Zr and Al, especially of Ti, are preferred as
metal compounds. Suitable metal compounds are, for example,
Ti(OC.sub.2H.sub.5).sub.4, Ti(O-n- or i-C.sub.3H.sub.7).sub.4,
Ti(OC.sub.4H.sub.9).sub.4, TiCl.sub.4,
Ti(O-iC.sub.3H.sub.7).sub.2Cl.sub.2, hexafluorotitanic acid,
TiOSO.sub.4, diisopropoxybis(ethylacetoacetato)titanate,
poly(dibutyltitanate), tetrakis(diethylamino)titanium,
titanium-2-ethylhexoxide, titanium
bis(triethanolamine)diisopropoxide, titanium chloride
triisopropoxide, Al(OC.sub.2H.sub.5).sub.3,
Al(O-sec.-C.sub.4H.sub.9).sub.3, AlCl(OH).sub.2,
Al(NO.sub.3).sub.3, Zr(OC.sub.3H.sub.7).sub.4,
zirconium-2-ethylhexoxide, BCl.sub.3, B(OCH.sub.3).sub.3 and
SnCl.sub.4,
Zr(OC.sub.3H.sub.7).sub.2(OOC(CH.sub.3)=CH.sub.2).sub.2, titanium
acetylacetonate, titanium oxide bis(pentane dionate),
Ti(OC.sub.3H.sub.7).sub.3(OOC(CH.sub.3)=CH.sub.2) and
Ti(OC.sub.2H.sub.4).sub.3(allylacetoacetate). Of the metal
compounds Ti(O-iC.sub.3H.sub.7).sub.4, Ti(OC.sub.4H.sub.9).sub.4,
titanium bis(triethanolamine)diisopropoxide and
Ti(OC.sub.3H.sub.7).sub.3(OOC(CH.sub.3)=CH.sub.2) are especially
preferred.
The hydrolysis and condensation to form the heterocondensate is
preferably carried out in two stages. In this case, the
hydrolysable silicon compound is subjected to a hydrolysis in a
first stage by mixing with water. The metal or boron compound is
added in a second stage when the silicon compounds have
substantially been hydrolysed.
The molar ratio of Si atoms of all the Si compounds used to the
metal atoms and boron atoms of all the metal and boron compounds
used and mentioned above can be selected within broad ranges, but
is preferably 10:1 to 1:3 and preferably 5:1 to 1:1.
For the organic compounds one or more organic monomers, oligomers
or polymers are used, which in each case have one or more,
preferably at least two polymerisable groups. Examples of
polymerisable groups are C.dbd.C-double bonds, hydroxy, amino,
carboxyl, acid anhydride groups, epoxide, isocyanate groups, acid
chloride groups, nitrile, isonitrile and SH groups, wherein
C.dbd.C-double bonds, such as vinyl, acrylic and methacrylic groups
are preferred. Polyisocyanates, melamine resins, polyester and
epoxide resins are suitable, for example, as polymers with free
polymerisable groups. Preferred examples are monofunctional,
bifunctional or polyfunctional acrylates and methacrylates.
Specific examples are diethyleneglycoldimethacrylate (DEGMA),
triethyleneglycoldimethacrylate (TEGDMA), bisphenol
A-glycidylmethacrylate (BisGMA), bisphenol A-diacrylate,
diurethanedimethacrylate, urethanedimethacrylate (UDMA),
Laromer.RTM.-acrylate from BASF, Ebecryl.RTM.,
pentaerythrittriacrylate (PETIA), hexanediol diacrylate,
trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,
neopentylglycoldimethacrylate, neopentylglycoldiacrylate, epoxy
acrylate resins, oligomer methacrylates, such as LR 8862, LR 8907
from BASF, or oligomeric urethane acrylates, such as UA 19T from
BASF.
The organic component is preferably added after adding the metal or
boron compound, preferably after maturation. The weight ratio of
all the inorganic components used, including the organic groups
contained therein, to the purely organic components used may, for
example, based on the hardened coating composition, be, for
example, 95:5 to 5:95 and preferably 80:20 to 20:80. The fillers
and/or pigments can optionally be added to the coating composition,
analogously to how this is described above for the alternative
layer.
The coating composition, which comprises an inorganic condensate
and an organic monomer, oligomer or polymer, which comprises at
least one polymerisable group, can be hardened after application to
the metallic or inorganic surface, for example thermally and/or
using conventional catalysts. The thermal hardening may, for
example, take place at temperatures above 40.degree. C. This
hardening can also take place at an elevated pressure.
The optional top layer in this case preferably comprises an
alkaline earth-free and/or alkali-free silicate. The production of
such inorganic, glass-like matrices or alkaline earth-free and/or
alkali-free silicate-containing matrices is known to the person
skilled in the art. This is especially preferably a matrix, which
is produced by the method and with the materials as described in
DE-A-10 2004 001 097 or DE 10 2010 011 185 A1.
The optional compressed alkali metal-free and alkaline earth
metal-free top layer comprises a matrix of an oxidated silicon
compound, for example a silicon oxide, a polysilicic acid or a
polysiloxane, in which additional components such as, for example,
pigments or fillers or other additives are optionally contained.
Alkali metal-free and alkaline earth metal-free in this case of
course contains alkali metal ion-free and alkaline earth metal
ion-free, i.e. the oxidated silicon compound of the top layer is
not an alkali silicate and/or alkaline earth silicate. The
expression alkali metal-free and alkaline earth metal-free does
not, of course, exclude traces of alkali metal ions and alkaline
earth metal ions in the top layer, which may, for example be
introduced by ionogenic impurities into the components used for the
coating composition. Thus, for example, the content of alkali may
be up to 0.2% by weight, for example, in Levasil.RTM., a silica
sol, which is stabilised by Na.sup.+ ions.
By adding Levasil.RTM. to the coating composition of the top layer,
although small quantities of alkali metal would therefore be
introduced, this does not lead to the formation of an alkali
silicate. Expressed differently, an alkali metal-free and alkaline
earth metal-free top layer or oxidated silicon compound means that
the atomic ratio of Si to (alkali metal and/or alkaline earth
metal) is greater than 500, especially greater than 1000.
In the silicon-oxide skeleton, some of the Si ions may optionally
be replaced by other ions such as, for example, Al but this is
generally not preferred. The top layer is obtainable by
wet-chemical application of a coating sol obtained by the sol-gel
method and the thermal compression of the coating sol (sol-gel
layer) generally after drying.
The coating composition for the optional top layer is, for example,
obtainable by hydrolysis and condensation of one or more silanes of
the general formula (I): R.sub.nSiX.sub.4-n (I) wherein the groups
X, the same or different from one another, are hydrolysable groups
or hydroxyl groups, the groups R, the same or different from one
another, stand for hydrogen, alkyl, alkenyl and alkinyl groups with
up to 4 carbon atoms and aryl, aralkyl and alkaryl groups with 6 to
10 carbon atoms and n signifies 0, 1 or 2, providing that at least
one silane wherein n is 1 or 2 is used, or oligomers derived
therefrom. The hydrolysis and condensation can optionally be
carried out in the presence of a) optionally added SiO.sub.2
particles, especially nano-scale SiO.sub.2 particles and/or b)
optionally of alkoxides or soluble compounds of the metals B, Al,
Si, Ge, Sn, Y, Ce, Ti or Zr.
The hydrolysate or condensate of hydrolysable compounds is
preferably a coating suspension or solution, especially preferably
a coating sol, which are produced by the sol-gel method or similar
hydrolysis and condensation processes.
The hydrolysable compounds preferably comprise at least one
organically modified hydrolysable silane. The hydrolysate or
condensate is especially preferably an alkali- or alkaline
earth-free coating suspension or solution and preferably an
alkaline earth-free or alkali-free coating sol.
Preferably used as the silicate-containing coating suspension or
solution is a coating composition, which is obtained by hydrolysis
and condensation of at least one organically modified hydrolysable
silane in the absence of alkaline metal or alkaline earth metal
oxides or hydroxides and optionally in the presence of nano-scale
SiO.sub.2 particles.
The silanes of formula (I) correspond to the silanes of formula (I)
used in the layer comprising an alkali silicate and/or alkaline
earth silicate. The detailed information listed there for the
silanes of formula (I) that can be used apply analogously here, as
long as nothing else is stated. The optional top layers generally
have a layer thickness of 1 to 15 .mu.m, preferably 4 to 12 .mu.m
and especially 6 to 10 .mu.m.
Both the coating composition for the layer used alone or as a base
layer and the optional top layer may contain additives that are
conventional in the paint industry, for example additives
controlling the rheology and the drying behaviour, wetting and
flow-control agents, defoamers, surfactants, solvents, dyes and
pigments, especially colouring pigments or effect pigments.
Furthermore, conventional commercial matting agents, for example
micro-scale SiO.sub.2 or ceramic powders may be added in order to
achieve matted layers with anti-fingerprint properties. If used,
the hydrolysis and polycondensation of the silanes can take place
in the presence of matting agents, for example micro-scale
SiO.sub.2 or ceramic powders. However, these may also be added
later to the coating composition.
Both the coating composition for the layer used alone or as a base
layer and also that for the optional top layer can be applied by
the conventional wet-chemical coating techniques, for example
dipping, casting, centrifuging, spraying, roller application,
brushing on, application by doctor blade or curtain coating.
Printing methods, such as, for example, screen printing can also be
used.
The coating composition applied to the metallic or inorganic
surface for the layer used as the single layer or base layer
comprising an inorganic, glass-like matrix of an alkali silicate
and/or alkaline earth silicate and for the optional top layer is
normally dried at room temperature or a slightly elevated
temperature, for example up to 100.degree. C., especially to
80.degree. C., before it is thermally compressed to form a
glass-like layer. The thermal compression can optionally also take
place by UV, IR or laser radiation.
When using the double layer, the procedure for compressing the
layers can be such that firstly the base layer is compressed
followed by the top layer or the two layers in the stack. If
nothing else is stated, the following details on the conditions of
the compression apply equally to the layer used as a single layer
or base layer comprising an inorganic, glass-like matrix of an
alkali silicate and/or alkaline earth silicate and to the optional
top layer, but not to the layer comprising an inorganic-organic
hybrid matrix.
The compression temperatures may vary within broad ranges and of
course also depend on the materials used. Suitable ranges are known
to the person skilled in the art. The thermal compression generally
takes place in the area at a temperature in the range from 300 to
800.degree. C., preferably from 350 to 700.degree. C. Owing to the
thermal compression, any organics optionally present are also
optionally combusted out completely or to a desired very low
residual content, so a glass-like inorganic layer is obtained. The
coating composition may, for example, on high-grade steel or steel
surfaces already be converted at relatively low temperatures,
generally from 400.degree. C., into dense SiO.sub.2 films or alkali
silicate and/or alkaline earth silicate films.
The layers can be thermally compressed both under a normal or
oxidising atmosphere and under protective gas or a reducing
atmosphere or with proportions of hydrogen. Especially, the layer
can be compressed under atmospheric or oxidising, inert or reducing
conditions or under such conditions changing one after the other.
The layer can be compressed in one or more stages. The thermal
compression can comprise two or more stages in different conditions
or those changing one after the other, which is generally also
preferred. The thermal compression can thus take place in a first
stage at an oxidising atmosphere and relatively low temperatures in
order to combust out the organics and then in a second stage at an
inert atmosphere and relatively high temperatures for the final
compression.
Thus, for example, compression can take place in the first stage in
an oxygen-containing atmosphere, for example on air or
alternatively in a vacuum, for example at a residual pressure
.ltoreq.15 mbar. The final temperature may be in the range from 100
to 500.degree. C., preferably 150 to 450.degree. C., the precise
temperatures depending inter alia on the selected conditions and
the desired further treatment.
During compression in oxygen-containing atmosphere it is preferred
to use compressed air as the process gas. In this case, 3 to 10
times the furnace interior volume of process gas is preferably
introduced per hour, the excess pressure in the furnace interior
being about 1 to 10 mbar, preferably 2 to 3 mbar. At the same time,
during this process step, the steam partial pressure in the process
gas can be adjusted by introducing water into the compressed air
stream before entering the furnace. Thus, the microporosity of the
precompressed, or else the finally compressed layer, can be
adjusted. To produce coatings that are to be completely compressed
at temperatures from 450 to 500.degree. C. it is preferred, for
example, to adjust a relative air humidity of the process gas of 50
to 100% at temperatures up to a range from 200 to 400.degree. C.,
especially preferably from 250 to 350.degree. C. (water quantity
based on the room temperature). The addition of water is stopped
for the further compression process up to the above-mentioned final
temperature of 450 to 500.degree. C.
In the second heat treatment stage, a further compression takes
place with the formation of a glass-like layer. The second heat
treatment stage is preferably carried out up to a final temperature
in the range from 350 to 700.degree. C., preferably 400 to
600.degree. C. and especially preferably 450 to 560.degree. C.
These temperature ranges are also preferred when the compression is
carried out in one step. The second stage preferably takes place in
a low-oxygen atmosphere or oxygen-free atmosphere with only a very
small oxygen content (.ltoreq.0.5% by volume). Work may, for
example, take place under normal pressure or in a vacuum. An inert
gas such as nitrogen with an excess pressure of 1 to 10 mbar,
preferably 1 to 3 mbar, can be used as the low-oxygen
atmosphere.
More than two compression stages can also be used. For example, it
may be expedient for a further compression stage under reducing
conditions, for example with forming gas, to follow the two
above-mentioned stages. Further details on suitable compression
stages and the respective conditions can also be found in
DE-A-102004001097 or DE 102010011 185 A1.
The thermal compression generally takes place according to a
controlled temperature programme, the temperature being increased
at a specific speed up to a maximum final temperature. The
above-mentioned temperatures for the compression relate to this
maximum final temperature. The residence times at the maximum
temperatures in the compression stages are generally 5 to 75 min
and preferably 20 to 65 min.
Thus glass-like layers can be obtained on metallic and also on
inorganic surfaces, which have a good anti-limescale effect, a high
hydrolytic resistance and high abrasion resistance. They also form
a hermetically sealing layer, which prevents or drastically reduces
the oxygen influx to the metallic or inorganic surface even at
relatively high temperatures and ensures excellent corrosion
protection and also helps to avoid soiling, for example due to
fingerprints, water, oil, grease, surfactants and dust. The same
advantages can be achieved if, instead of the layer comprising an
inorganic, glass-like matrix of an alkali silicate and/or alkaline
earth silicate, a layer or base layer comprising an
inorganic-organic hybrid matrix is used.
One or more intermediate layers can optionally be provided between
the metal surface or inorganic surface and the anti-limescale
coating, for example in order to improve the adhesion or in order
to ensure an additional protection. Inorganic, glass-like layers
are generally used for this. The intermediate layers can also be
applied wet-chemically or by other methods, such as, for example,
CVD or PVD, wherein they can be compressed separately or preferably
together with the anti-limescale coating. The conditions which were
described above for the anti-limescale coating can be used as the
conditions for thermal compression but, depending on the
composition, other conditions may also be expedient.
The object or material, which is provided with the anti-timescale
coating, with a metal surface or inorganic, especially ceramic or
mineral surface, can be a semi-finished product, such as plates,
metal sheets, pipes, rods or wires, a component or a finished
product. It can be used for systems, tools, domestic equipment,
electric components, machines, vehicle parts, especially car parts,
production systems, facades, conveying tools, safety valves, pipe
lines, heat exchangers or parts thereof.
The anti-limescale coating is, especially, suitable for objects or
materials with a metal surface such as metal housings of electronic
equipment, metallic components for optical equipment, metallic
parts of vehicles in the internal and external area, metallic
components in mechanical engineering and systems engineering,
motors, metallic components of medical equipment, metallic
components of household equipment, other electric equipment and
turbines, domestic equipment such as, for example, containers,
knives, metal facade components, metal components of lifts, parts
of conveying devices, metallic parts of furniture, garden
equipment, agricultural machines, fittings, motor components and
production systems in general and, especially, for pipe lines, sand
control systems and safety valves in the conveyance or storage of
oil and gas.
Sand control systems are used in the conveyance of oil or gas so
that sand or other solid impurities are kept back during
conveyance. For this purpose, the sand control systems contain, for
example, gravel packs, packs of ceramic particles or proppants,
generally moulded bodies made of sand. The anti-limescale coating
system according to the invention is surprisingly also suitable for
coating mineral objects or materials, ceramic particles or rocks,
such as gravel, grit or sand, especially for gravel packs, packs of
ceramic particles and proppants such as are used as sand control
systems.
The object with at least one metal surface or inorganic surface is
especially preferably a storage or transport device for water or
media containing water, the anti-limescale coating being able to be
applied to at least one metal surface or inorganic surface of the
storage or transport device. This storage or transport device is
preferably a boiler, a tank, a pipeline or a valve for water or
media containing water, a pipeline and a safety valve being
especially preferred.
The medium containing water is preferably a water-containing crude
oil or natural gas. Such oils and gases containing water occur, for
example, in oil or gas conveyance or oil or gas storage. The
storage or transport device is therefore especially preferably a
pipeline, a sand control system (gravel pack, proppants) or a
valve, especially a safety valve, in the conveyance of oil or gas
or storage of oil or gas. Owing to the anti-limescale coating, the
limescale deposit in oil or gas pipes used to convey or store crude
oil or natural gas, in safety valves or sand control systems
belonging to the line system, can be significantly reduced or even
completely prevented.
The invention accordingly also relates to a method for transporting
or storing water or a medium containing water, in which the water
or the medium containing water is transported by an object or is
stored in an object, the object having the described anti-limescale
coating on at least one metal surface or inorganic surface.
The invention will be further described by the examples below,
which are not to restrict the invention in any way.
EXAMPLE 1 (DOUBLE LAYER SYSTEM)
Base Layer
25 ml (124.8 mMol) methyltriethoxysilane (MTEOS) are stirred with 7
ml (31.4 mMol) tetraethoxysilane (TEOS) and 0.8 g (20 mMol) sodium
hydroxide overnight (at least 12 hours) at room temperature until
the entire sodium hydroxide has dissolved and a clear yellow
solution is present. 3.2 ml (177.8 mMol) water are then slowly
dripped in at room temperature, during which the solution heats up.
Once the addition of water has ended, the clear yellow solution is
stirred at room temperature until it has cooled again, and it is
then filtered by means of a filter with a pore size of 0.8
.mu.m.
Production of a Coating Solution with Pigments
4 g of the red pigment LavaRed.RTM. from the company Merck AG are
dispersed in the presence of 8 g butylglycol as a
compatibiliser/surface modifier and levelling agent in 80 g of the
base layer system with powerful stirring.
In the process, an agglomerate-free dispersion having a viscosity
of about 15 mPas is achieved at 23.degree. C. which is suitable for
use in an automatic spray coating system.
Top Layer System
65.5 g MTEOS and 19.1 g TEOS are mixed and divided into two halves.
14.2 g Levasil 300/30 and 0.4 ml HCl (37%) are added to one half
while stirring (until the clear point is reached). The second half
of the silane mixture is then added. This mixture is allowed to
stand overnight. For activation, water is added to the batch (10%
by weight) (adjustment of the ROR to 0.8).
Application and Hardening of the Layers
Base layer: as the base layer, the coating solution with pigments
is applied to a metal substrate by means of spraying in such a way
that the wet film thickness is about 15 .mu.m. The layer is then
heated to 450 to 550.degree. C. depending on the metallic substrate
used.
Top layer: the top layer is applied by means of spraying with a wet
film thickness of about 10 .mu.m. The layer is then heated to 450
to 550.degree. C. depending on the metallic substrate.
EXAMPLE 2 (DOUBLE LAYER SYSTEM)
Base paint: 25 ml (124.8 mMol) methyltriethoxysilane (MTEOS) are
stirred with 7 ml (31.4 mMol) tetraethoxysilane (TEOS) and 0.8 g
(20 mMol) sodium hydroxide overnight (at least 12 hours) at room
temperature until the entire sodium hydroxide has dissolved and a
clear yellow solution is present. 3.2 ml (177.8 mMol) water are
then slowly dripped in at room temperature until the solution heats
up. After the addition of water has ended, the clear yellow
solution is stirred at room temperature until it has cooled again
and it is then filtered by means of a filter with a pore size of
0.8 .mu.m.
Pigment suspension (a): a mixture of 50% by weight Alusion
Al.sub.2O.sub.3 (platelet-shaped corundum, particle size
d.sub.90=18 .mu.m) in 2-propanol is homogenised in a dispermat for
15 minutes while cooling at 20.degree. C. and the content of the
suspension is then determined by vaporising a sample of the end
product (solid content 40.0% by weight).
Pigment suspension (b): a mixture of 50% by weight F1000
Al.sub.2O.sub.3 (blasting corundum, broken, particle size 1 to 10
.mu.m) in 2-propanol is homogenised in a dispermat for 10 minutes
while cooling and the content of the suspension is then determined
by vaporising a sample of the end product (40.0% by weight).
Coating Paint
To produce the coating paint 0.9 kg of the base paint are prepared
and then 100 g ethylene glycol monobutyl ether are added and
stirred. 30 g pigment suspension (a) and 45 g pigment suspension
(b) are added while stirring and stirring takes place for a further
20 minutes.
Coating
After filtration by means of a 100 .mu.m filter screen, the coating
paint (single layer) is sprayed on in an industrial flat spraying
system to a wet film thickness of 11 .mu.m onto the high-grade
steel parts pre-cleaned in a conventional commercial alkaline
cleaning bath and then dried at room temperature for 15
minutes.
Following the coating, the coated parts are introduced into a
retort furnace that can be evacuated, hardened in a first heating
step at 200.degree. C. in air and then in pure nitrogen at
500.degree. C. in 1 h. The hardened glass layer has a layer
thickness of 4 .mu.m.
Test for Anti-Limescale Effect
The metal substrates with an anti-limescale coating produced in
Examples 1 and 2 were subjected to the following test. For
comparison, the test was also carried out with the metal substrates
without an anti-limescale coating used in Examples 1 and 2.
1.23 g Ca(OH).sub.2 were dissolved in 1000 ml distilled water at
room temperature. CO.sub.2 was introduced into the saturated
solution until no further CaCO.sub.3 precipitation occurs. The
coated or uncoated sample was immersed in the solution in a
desiccator for 3 days at 85.degree. C. In order to ensure that the
sample is completely immersed, the CaCO.sub.3 suspension is filled
up daily. Once the immersion time had expired, the sample was
removed, rinsed with water and the layer and the quantity of
CaCO.sub.3 deposited thereon were evaluated. The evaluation leads
to the result that the layer is completely intact. Adhesion tests
produce a result of GT/TT=0/0. With regard to the anti-limescale
effect, the uncoated comparison samples exhibit a clear limescale
residue after rinsing with water. The coated sample exhibits no
limescale residues after rinsing.
* * * * *